This is a really important question. If you want fat loss or muscle gain, or a combination of both, you'll want to know you're heading in the right direction. If not, a change of tact would be advised. Track progression down the line, did that change work? And so forth, this is how you're going to get those results you want.
You don't want any muscle gain or fat loss? Then you're doing fine. However, if you do, then we need to make sure you're tracking your progress. In your job, you put the hours in, you get paid. In the gym, you put your hours in, have you lost fat or gained muscle? There are a few ways in which we can do this.
Photos
We've all seen them. The before and after pictures. They are THE way, in my opinion. Take them weekly, on the same day each week, the same time, in front of the same full length mirror, in the same underwear, after going to the toilet, before eating anything or drinking anything. Hopefully the lighting will be roughly the same. Take a front-on picture, take a side-on picture and back picture. Compare weekly. If you're going the right way, you'll probably start to see some changes in around 3-4 weeks, which will of course differ individually. I tell you what, when you start to see those changes... You will feel so, so motivated! You know you're going the right way, and those sessions in the gym will just feel great. I'm also talking from personal experience. So if you're not doing this already, I recommend you give this a go. If you are already very lean or very muscular, the results are going to be slower than someone who isn't as lean or muscular.
So, er, first of all. Sorry. I am not a big fan of personal trainers constantly half naked, or mostly naked. But yeah, this is my progression in a flexed state stood to the side (yes, I have to flex for my abs to show). Left to right were taken over a period of 5 months. Definition changed much more at the start, the last couple months have been way more subtle. I would have no idea how much leaner I'd have gotten, especially in these last couple of months without taking photos. I've lost roughly 8-10kg in the time from March to September. I also have to bear in mind I haven't been able to train like I used to thanks to an annoying back injury. So I've probably lost a bit of muscle and strength, but that's out of my control.
Clothes
The next best thing after photos. Most people own a pair of jeans, or some sort of clothing that is particularly tight, or they used to fit in to. If they are looking to lose fat and get lean, then these will eventually fit looser and you know you're doing it right. If you are looking to put on muscle, this can also work really well. You will fill out your jeans, fill out your top, and require new clothes to fit those bigger muscles.
I've noticed my clothes are much looser. I don't fill out the belly region of all my tops anymore. My jeans fit much better. Tying up my shoe laces isn't such a struggle, which it genuinely was when I got to my biggest.
Scales
I'm not a fan of scales. People get obsessed with scales and their numbers, that's my issue with them. If you start to think you're not going the right way because you're 'heavier' (I put heavier in quotes, because you have no idea what you're weighing each time you step on the scales) yet your photos and clothes are showing you're doing it all correctly, then get off those damn scales because they aren't telling you anything.
HOWEVER... IF you REALLY want to keep weighing yourself, and you're not someone who has a bad relationship with their weight, then I advise you do it meticulously. Similar to the way you would take photos, you'll weigh yourself every morning, after going to the toilet, don't drink any water or have any food before it. That's not how much you weigh. Do that every morning for a month and take the mean weight. That's roughly what you weigh. From month to month compare the mean, and then you could argue you are going the right or wrong way using scales, but I would only EVER advise you do that in conjunction with clothes and photo tracking.
You have to consider many things when you step on the scales. You literally don't know what you are weighing. Muscle is good weight. Fat is not so good weight. The scales weigh it all. Are you bloated? Is it that time of the month (women, obviously)? Did you eat a lot yesterday? Did you drink a lot yesterday? Did you have a lot of salt? Did you eat a lot of one particular macro? Did you have a rather large bowel movement yesterday?
Too many variables for an accurate measure. I don't like scales for this reason.
There are MANY ways to track progression that all work well
1. Weights increasing - Are the weights you are lifting increasing in the same rep range? Yes? Then you are progressing.
2. Time under tension/load - Is the duration that you spend during a set lifting increasing? Yes? Then you are progressing.
3. Distance - Are you running/swimming/rowing/cycling further? Yes? Then you are progressing.
There are many other ways and I could go on, but you get the idea. Keep everything goal-orientated when you look at it. If you keep increasing your running distance beyond 10km yet all you are training for is a 10km run, then that's not really very specific to your goals.
Do I have to track progression?
No. If you are quite happy with how you are going, yet you're not tracking it, carry on. So long as you are happy and enjoying yourself!
I don't know If I'm progressing and I'd like to know
If you aren't sure you are progressing, you're not quite sure your workouts are getting you to your goals, then first of all consider your goals, and if photos and clothing will help you track whether or not you are getting to your goals, then use them. If you really want to use scales, fine, just use them with clothing and photo tracking as well.
Good luck and thanks for reading!
BennyFit